This invention relates to an improved polymeric composition which is crosslinked to produce flame and heat resistant products for both electrical and nonelectrical uses. More particularly, the invention relates to a crosslinkable flame retardant polymer containing a novel coupling agent and inorganic hydrate filler.
Fire resistant compositions are widely used for wire and cable insulation, among other uses. In electrical environments, both insulating and flame resistant properties are essential. That is, the compositions when ignited should not exhibit after glow, should not emit noxious or toxic smoke, and should promote the formation of an inorganic char which is both non-combustible and non-toxic. Additionally, the compositions desirably should not deteriorate over long service times.
In some instances, the manufacture of extrudable fire resistant compositions requires the use of halogenated polymers such as chlorinated polyethylene, chlorosulfonated polyethylene, polyvinyl chloride, and chlorobutadiene, or coatings of chlorinated polymers over other polymer compositions. However, in fire situations, such chlorinated compositions evolve toxic hydrogen chloride gas and emit large quantities of noxious smoke. As smoke inhalation is an even greater cause of death in fires than the fire itself, such products are unsuitable. Further, hydrogen chloride gas is a highly corrosive gas which is converted quickly into hydrochloric acid in the presence of any water. Exposure to hydrochloric acid will damage or destroy electrical equipment such as computers, switchboards, printed circuits, and the like.
One widely used fire retarding insulation product has been a crosslinkable copolymer of ethylene and vinyl acetate, one or more hydrated inorganic fillers, one or more silane coupling agents, and a crosslinking agent (typically an organic peroxide). Such a product is taught in North and Kuckro, U.S. Pat. Nos. 3,832,326 and 3,922,442. Similar products are also taught in Biggs et al, U.S. Pat. Nos. 4,349,605 and 4,381,362. Compositions of this type are used as fire retardant insulation and jacketing for copper and aluminum conductors and in instrument transformers. The products exhibit good processability and meet SAE J-1128 low tension primary cable standards.
One problem with the manufacture of these crosslinkable polymers has been the need for the use of relatively expensive silane coupling agents. Such silanes are required to provide compatibility between the polymer and inorganic fillers so that a well-dispersed, homogeneous composition will be produced.
Accordingly, there still exists a need in this art for an inexpensive flame and heat resistant polymer composition which also provides electrical insulating properties and which, when ignited, does not emit noxious smoke or corrosive gases.